1. Field of the Invention
The present invention relates to an exhaust gas dilution apparatus used for measuring particulate emissions discharged from diesel engines and the like.
2. Description of the Background Art
A mini-tunnel system is given as a conventional exhaust gas dilution apparatus. According to this system, part of the exhaust gas from a diesel engine, for example, is removed and mixed with air in a dilution tunnel to produce and measure particulate emissions. It is important for this type of dilution apparatus to constantly segregate a certain proportion of the exhaust gas and to introduce such segregated gas into the dilution tunnel. An axisymmetric flow division system (Japanese Patent Application Laid-open No. 9-325102, etc.) has been proposed for this purpose.
FIG. 10 is a schematic drawing showing an example of a conventional exhaust gas dilution apparatus of this axisymmetric flow division system. This exhaust gas dilution apparatus 100 has a rectifier 101, a divider 102, a surge tank 104, a dilution tunnel 105, and the like.
The rectifier 101 adjusts the flow of exhaust gas from the engine exhaust pipe and introduces the gas into the divider 102.
The divider 102 divides the introduced exhaust gas into a plurality of flows by means of divider pipes 103 and extracts part of the gas to outside. This divider 102 is provided with a plurality of divider pipes 103 having the same length and diameter. Exhaust gas introduced into the divider 102 is divided by flowing into these divider pipes 103. A surge tank 104 is an exhaust chamber installed at the end of the divider 102 to recombine the gas flows divided by the divider 102 and discharge the combined gas.
An introduction pipe (a divider pipe on the dilution tunnel side) 103t is one of the divider pipes 103, which is folded outwardly from the divider 102 and extends to the dilution tunnel 105. Gas flowing into the introduction pipe 103t is led to, and discharged into the dilution tunnel 105. The dilution tunnel 105 is an air duct for diluting the exhaust gas introduced by the introduction pipe 103t. 
Because this system can divide the exhaust gas in a specified ratio according to the physical form of the divider 102, this type of exhaust gas dilution apparatus can divide gas more accurately than other conventional method such as a twin venturi type or multi-pipe type.
The aforementioned exhaust gas dilution apparatus shown in FIG. 10, however, cannot accurately divide the exhaust gas when the pressure Pc in the surge tank (exhaust chamber) 104 and the pressure Pt in the dilution tunnel 105 are not equivalent.
An object of the present invention is to overcome the above problems and to provide an exhaust gas dilution apparatus which can accurately divide the exhaust gas.
In order to attain the above object, a first invention provides an exhaust gas dilution apparatus equipped with a divider which divides exhaust gas introduced therein into a plurality of flows, extracts a portion of the gas to a dilution tunnel, and discharges the remaining portion to an exhaust chamber, wherein the exhaust gas dilution apparatus is characterized by comprising a first pressure detection means to detect the pressure in the dilution tunnel, a second pressure detection means to detect the pressure in the exhaust chamber, an exhaust adjustment means to adjust the exhaust gas in the exhaust chamber, and a control means to control the exhaust adjustment means so that the output of the first pressure detection means and the output of the second pressure detection means may become equivalent.
A second invention comprises an exhaust gas dilution apparatus equipped with a first divider which divides exhaust gas introduced therein into a plurality of flows and has a first divider pipe for extracting a portion of the gas into a dilution tunnel and a second divider pipe to discharge the remaining portion to an exhaust chamber, wherein the exhaust gas dilution apparatus is characterized by comprising a first and second flow rate measuring means having equivalent performance, provided in an equivalent position respectively in the first and second divider pipes, an exhaust adjustment means for adjusting exhaust from the exhaust chamber, and a control means to control the exhaust adjustment means so that the flow rate on the dilution tunnel side measured by the first flow rate measuring means and the flow rate on the exhaust pipe side measured by the second flow rate measuring means may become equivalent.
A third invention is the exhaust gas dilution apparatus having the same constitution as the exhaust gas dilution apparatus of the second invention, provided that the second flow rate measuring means comprises a plurality of venturis, one provided in each of the second dividers, a plurality of pressure difference detectors for measuring the pressure difference between the high pressure side and the low pressure side of each venturi, and an averaging circuit which averages the electric signals detected by the pressure difference detectors.
A fourth invention is an exhaust gas dilution apparatus having the same constitution as that of the second invention, provided that the second flow rate measuring means comprises a plurality of venturis for measurement, provided in representative dividers selected from the plurality of second dividers, and dummy venturis which are provided in the plurality of second dividers, excluding the dividers for which the venturis for measurement are provided, and have a throttle with the same configuration as that provided in the venturis for measurement.
A fifth invention is an exhaust gas dilution apparatus having the same constitution as that of the second invention, provided that the second flow rate measuring means comprises a plurality of venturis, one provided in each of the second dividers, and one pressure difference detector for measuring the pressure difference between the high pressure side and the low pressure side in combined pressure introduction pipes on the high pressure side and the low pressure side, which are formed by respectively combining the pressure introduction pipes of the venturis on the high pressure side and on the low pressure side.
A sixth invention provides an exhaust gas dilution apparatus equipped with a divider which divides exhaust gas introduced therein into a plurality of flows and has a first divider pipe for extracting a portion of the gas into a dilution tunnel and a second divider pipe for exhausting the remaining portion into an exhaust chamber, wherein the exhaust gas dilution apparatus is characterized by comprising first and second fluid throttling means having equivalent performance, provided in an equivalent position respectively in the first and second divider pipes, a high pressure side pressure difference detection means for detecting the pressure difference between the high pressure side of the first fluid throttling means and the high pressure side of the second fluid throttling means, a low pressure side pressure difference detection means for detecting the pressure difference between the low pressure side of the first fluid throttling means and the low pressure side of the second fluid throttling means, an exhaust adjustment means to adjust exhaust from the exhaust chamber, and a control means to control the exhaust adjustment means so that the pressure difference values detected by the low pressure side pressure difference detection means and the high pressure side pressure difference detection means may become equivalent and zero.
A seventh invention is an exhaust gas dilution apparatus having the same constitution as that of the sixth invention, provided that the high pressure side pressure difference detection means and the low pressure side pressure difference detection means are equipped with a cylinder, a free piston slidably inserted into the cylinder, and a piston position detecting means which detects the position of the free piston.
An eighth invention is an exhaust gas dilution apparatus having the same constitution as that of the first, second, or sixth invention, provided that the exhaust adjustment means is equipped with a suction which removes the gas in the exhaust chamber from downstream and an air introducing part which is provided between the exhaust chamber and the suction for introducing the atmospheric air.
A ninth invention is an exhaust gas dilution apparatus having the same constitution as that of the first invention, but further provided with a monitor means to continuously monitor the pressure values obtained by the first and/or second pressure detection means.
A tenth invention is an exhaust gas dilution apparatus having the same constitution as that of the first invention, but further comprising a result decision means which decides whether the pressure difference obtained by the first and second pressure detection means is within a previously specified range of deviation or above a previously specified correlation coefficient during a period of measurement, or decides, based on that result, whether the divider exhibits flow division performance within a permissible accuracy.
An eleventh invention is an exhaust gas dilution apparatus having the same constitution as that of the second invention, but further comprising a monitor means to continuously monitor the flow rate obtained by the first and/or second flow rate measuring means.
A twelfth invention is an exhaust gas dilution apparatus having the same constitution as that of the second invention, but further comprising a result decision means which decides whether the flow rate difference obtained by the first and second flow rate measuring means is within a previously specified range of deviation or above a previously specified correlation coefficient during a period of measurement, or decides, based on the results, whether the divider exhibits flow division performance in permissible accuracy.
A thirteenth invention is an exhaust gas dilution apparatus having the same constitution as that of the sixth invention, but further comprising a monitor means to continuously monitor the pressure difference obtained by the high pressure side pressure difference detection means and/or low pressure side pressure difference detection means.
A fourteenth invention is an exhaust gas dilution apparatus having the same constitution as that of the sixth invention, but further comprising a result decision means which decides whether the pressure difference obtained by the high pressure side and low pressure side pressure difference detection means is within a previously specified range of deviation or above a previously specified correlation coefficient during the period of measurement, or decides based on that result whether the divider exhibits flow division performance in permissible accuracy.
A fifteenth invention provides an exhaust gas dilution apparatus equipped with a divider which divides exhaust gas introduced therein into a plurality of flows and has a first divider pipe for extracting a portion of the gas into a dilution tunnel and a second divider pipe for exhausting the remaining portion to an exhaust chamber, wherein the exhaust gas dilution apparatus is characterized by comprising first and second flow rate measuring means having equivalent performance, provided in an equivalent position respectively in the first and second divider pipes, a fixed volume sampling means provided downstream of the dilution tunnel to cause the divided exhaust gas and dilution gas to flow at a constant rate and collect samples, a gas circulation means to recycle exhaust gas from the fixed volume sampling means to upstream of the divider during the time when the engine to be measured is not operating, and a correction means to correct the flow dividing precision of the divider based on the flow rate on the dilution tunnel side measured by the first flow rate measuring means and the flow rate on the exhaust pipe side measured by the second flow rate measuring means.
A sixteenth invention provides an exhaust gas dilution apparatus equipped with a divider which divides exhaust gas introduced therein into a plurality of flows and has a first divider pipe for extracting a portion of the gas into a dilution tunnel and a second divider pipe for exhausting the remaining portion to an exhaust chamber, wherein the exhaust gas dilution apparatus is characterized by comprising first and second fluid throttling means having equivalent performance, provided in an equivalent position respectively in the first and second divider pipes, a high pressure side pressure difference detection means for detecting the pressure difference between the high pressure side of the first fluid throttling means and the high pressure side of the second fluid throttling means, a low pressure side pressure difference detection means for detecting the pressure difference between the low pressure side of the first fluid throttling means and the low pressure side of the second fluid throttling means, a fixed volume sampling means provided downstream of the dilution tunnel to cause the divided exhaust gas and dilution gas to flow at a constant rate and collect samples, a gas circulation means to recycle exhaust gas from the fixed volume sampling means to upstream of the divider during the time when the engine to be measured is not operating, and a correction means to correct the flow dividing precision of the divider based on the pressure difference value detected by the high pressure side pressure difference detection means and the low pressure side pressure difference detection means.
A seventeenth invention provides an exhaust gas dilution apparatus equipped with a divider which divides exhaust gas introduced therein into a plurality of flows, extracts a portion of the gas to a dilution tunnel, and discharge the remaining portion to an exhaust chamber, wherein the exhaust gas dilution apparatus is characterized by comprising a fixed volume sampling means provided downstream of the dilution tunnel to cause the divided exhaust gas and dilution gas to flow at a constant rate and collect samples, and a gas circulation means to recycle exhaust gas from the fixed volume sampling means to upstream of the divider during the time when the engine to be measured is not operating.